Sadly, on my last trip to my hometown in NJ, I walked to my old fave fishing spot only to find a small school of large KOI swimming in the lake. That lake did house wild Carp but these were definitely aquarium Koi not wild Carp.
I just saw something on TV here as well about the goldfish explosion in the CO lake. Not surprising to me. Come to FL and go to any canal in S. FL and you will see a variety of aquarium fish that are the byproduct of hobbyist releases. In some places, it's easier to catch an Oscar than it is to catch a Largemouth Bass.
In other places, you can catch more African Cichlids than Native panfish. You can see a list of what's here on this site: Nonnative Freshwater Fish
Then there's the saltwater fish as well.